Horizontal Directional Drilling

The Use of Horizontal Directional Drilling to Install Underground Pipes

Before the development of the technique known as horizontal directional drilling (HDD), the only way to install an underground pipeline would have been to start by digging a trench. In the next step, the sections of pipework must be positioned in the trench and connected, and the assembled structure reburied. Although this method is still used today, it is a slow, labour-intensive process which, in addition to carrying a substantial price tag, also tends to be unnecessarily disruptive.

Directional DrillingWhile this might be an acceptable option when laying pipes under a field in some rural setting, it is far from practical when required to burrow beneath a busy highway, an airport runway, or a row of private residences. In such cases, horizontal directional drilling offers a cheaper, faster, and more environmentally friendly alternative.

Before starting to drill, the proposed route of an underground pipeline must be surveyed to identify any possible obstacles that might require a diversion. In some cases, ground-penetrating radar may be used to detect subterranean obstructions. With the route mapped out, the HDD process can proceed. Let’s say, for example, the project goal is to pipe water from a nearby lake to use in a sprinkler system for a golf course.

The horizontal directional drilling process employs a special rig with a steerable drill bit. Its angle of attack can be controlled from the surface by means of a built-in servo using either a wireless or a cabled connection. Once the rig has been inserted into the ground at a shallow angle and reached the planned depth, the drill bit is adjusted to move horizontally and to follow the proposed route. Its progress can be monitored on foot from above with the help of suitable sensing equipment.

Should the drill bit encounter an obstruction, its progress will be slowed, indicating the need to adjust the horizontal directional drilling process so as to bypass the obstruction. On reaching the lake, the process will have provided a narrow boring that is still too small to accommodate a pipeline. At this point, a back reamer is attached to the drill bit and the direction of travel is reversed. The action of the reamer is to enlarge the borehole sufficiently to accommodate the pipe, which can then be pulled into position in a similar fashion. The golf course will now have the source for its sprinkler system without any visible evidence of the underground incursion.

The horizontal directional drilling process requires both specialised equipment and personnel to operate it. HPD Drilling is widely recognised by industries in South Africa as a leader in this increasingly important field.